PROJECT SUMMARY Progress in understanding the causes of Alzheimer's disease is severely hampered by the lack of translational animal models that accurately recapitulate age-associated changes that occur within the human central nervous system (CNS). Like humans, however, rhesus macaques (Macaca mulatta) are long-lived diurnal primates that show similar neuroendocrine changes during aging, as well as perturbed sleep-wake cycles and cognitive decline. Furthermore, there is evidence that the brains of old rhesus macaques show some of the same pathological hallmarks of Alzheimer's disease as do humans, including amyloidosis and taupathology. Importantly, unlike humans, rhesus macaques can be maintained under tightly controlled environmental conditions, such as photoperiod, temperature and diet, and their brains can be collected with zero postmortem interval. Therefore, the primary goal of the proposed study is to build on our previous in vivo research using Indian-origin rhesus macaques, and to help elucidate the molecular mechanisms that underlie early stages of Alzheimer's disease pathology and cognitive decline. We propose to examine the effect of age, sex and hormone status on neuropathological markers in brain areas that are especially susceptible to Alzheimer's disease pathology, including the prefrontal cortex (PFC), entorhinal cortex (ERC) and amygdala (AMG), as well as in a brain area that is relatively resistant to neurodegeneration (e.g., the cerebellum), and to correlate these developments with gene expression profiles and epigenetic signaling in the same brain areas. In addition, we propose to correlate these gene expression patterns with cognitive performance, sleep quality and neuronal connectivity. Under normal circumstances, such a study would not be feasible to perform (i.e., due to scarcity of old animals, prohibitive cost, excessive time and effort). On the other hand, we have already collected all of the necessary postmortem tissues from the following unique groups of animals that were previously characterized in terms of their cognitive performance, circadian activity and sleep quality: (1) Young females (2) Old females (3) Old ovariectomized females (4) Old ovariectomized females (supplemented with estrogen) (5) Young males (6) Old males (7) Old males (supplemented with androgens) Aim 1 will use immunohistochemistry to characterize the distribution and intensity of amyloid ? (A?), tau, apolipoprotein E (ApoE), GFAP and microglia in the PFC, ERC, AMG and cerebellum. Aim 2 will use RNA-seq to profile gene expression in the same brain areas, while Aim 3 will examine epigenetic signaling. Aim 4 will focus on the analysis of structural and connectivity differences within the CNS, using previously acquired MRI scans. The proposed study will be the first comprehensive characterization of central gene expression changes, epigenetic signaling and the connectosome of a highly-translational animal model of human aging, and should thereby help to disclose events that predispose individuals to development of Alzheimer's disease.